Rising power densities of electronics has called for more advanced cooling solutions. In harsh environment electronics, thermal management is especially challenging due to reliability and geometric constraints. Heat pipes and other two phase cooling methods are promising passive thermal management technologies. This work explores a designer working fluid for use in phase change heat transfer devices. Different fluids are tested in a flat grooved heat pipe. The surface augmentation created by using these fluids is studied with microscopic imaging and elemental analysis. The performance results show enhancements over water and the surface characterization confirms previous chemical analysis, lending insight into the optimization process for these fluids.978-1-4799-8600-2/15/$31.00 ©2015 IEEE 31st SEMI-THERM Symposium